As IT products have become more sophisticated, in order to process a larger amount of data in a short period of time, bits of data to be transmitted at a time have been increased, and a clock frequency has been increased. Recently, parallel transmission has been shifted to serial transmission (one-to-one transmission).
In the serial transmission, the clock frequency has been further increased to the Gbps band. A method of transmission has been shifted from conventional serial end transmission to differential transmission. The present invention proposes a structure of a transmission circuit board suitable for the differential transmission.
Non-Patent Reference 1 and Patent Reference 1 have disclosed a series of terminal portions (so-called foot pattern) formed on circuit board surfaces as a land suitable for such an application.
In Non-Patent Reference 1, as shown in FIG. 8(A), in a transmission circuit board with multi-layered signal layers, one signal layer has terminal portions in a two-row nine-column pattern. It is claimed that pairs of terminal portions 51 in a row direction are arranged alternately at one row to an adjacent row, so that it is possible to obtain an effect by drawing an equal path length of wiring portions 52 (pattern) of the terminal portions constituting P/N.
In a principle structure disclosed in Patent Reference 1, as shown in FIG. 8(B), a series of terminals in a seven-row nine-column pattern is divided into three signal layers, i.e., a first layer to a third layer. The structure in Patent Reference 1 is not limited to the differential transmission. When the structure is applied to the differential transmission as shown in FIG. 8(B), wiring portions are shifted with each other and drawn, thereby making it possible to properly arrange the terminal portions and the wiring portions for reducing the number of the signal layers.
When the structures disclosed in Non-Patent Reference 1 and Patent Reference 1 are combined, as shown in FIG. 9, terminal portions in an eight-row pattern, for example, are arranged to be differential pairs in a row direction. Wiring portions are arranged in a column direction to form four signal layers.
Non-Patent Reference 1: U.S.A. Altera Technical Bulletin “Board Design Guidelines for LVDS Systems” (July, 2000)
Patent Reference 1: Japanese Patent Publication No. 11-74399
When a pattern of a transmission circuit board is configured with the method disposed in Non-Patent Reference 1 or Patent Reference 1, it is possible to obtain multi-layered signal layers suitable for the differential pair. However, when the number of the signal layers increases, there is a room for improvement in terms of increased manufacturing cost and an increased thickness of the substrate as a product.
An object of the present invention is to provide a transmission circuit board applicable to the differential pair and capable of reducing the number of signal layers. Further, an object of the present invention is to provide a connector device having a connector connected to the transmission circuit board.